Cold sintering process with DMSO as a transient liquid for efficient improvement of thermoelectric properties in silver selenide

Abstract

This study investigates the enhancement of thermoelectric properties in silver selenide (Ag₂Se) via the cold sintering process (CSP) using dimethyl sulfoxide (DMSO) as a transient liquid phase. Unlike conventional sintering methods that require high temperatures and long processing times, CSP with DMSO enables densification at significantly lower temperatures while simultaneously tuning the microstructure and carrier transport properties. Bulk Ag₂Se samples were fabricated with varying DMSO concentrations (5–12 %) and sintering temperatures (190 °C, 220 °C, and 250 °C) to evaluate the influence of these parameters on thermoelectric performance. X-ray diffraction (XRD) analysis confirmed the retention of the orthorhombic β-Ag₂Se phase across all samples, with slight morphological changes observed due to DMSO concentration and sintering temperature. Optimal results were achieved at a DMSO concentration of 10 %, where a balance between electrical conductivity (σ) and Seebeck coefficient (S) yielded a high power factor. Thermal conductivity (κ) analysis showed a significant reduction attributed to enhanced phonon scattering from defects introduced via CSP with DMSO. Furthermore, the AS-DMSO250 sample (with 10 % DMSO and sintered at 250 °C) exhibited a stable ZT, ranging from 0.94 at 300 K to 1.10 at 380 K representing a 42–49 % enhancement over the reference sample, which had ZT values of 0.66 at 300 K and 0.74 at 380 K. The average ZT of the optimized sample with DMSO reached approximately 1.02 at 300–380 K, surpassing values commonly reported in the literature. These findings emphasize the critical role of DMSO concentration and sintering temperature in optimizing thermoelectric properties, offering a practical approach for advancing Ag₂Se-based thermoelectric materials for efficient energy harvesting near room temperature.